A moment later, the first of two deadly blasts threw the couple, who live in Boston, to the ground and sent pain searing through Cates’s now-bloodied right leg. Her calf was nearly blown off.

Fearing a second blast, her boyfriend, 41-year-old Leo Fonseca, threw himself on top of her injured body. As Fonseca frantically debated what to do next, his attention was snatched by the sound of a second bomb exploding in the distance. Next came Cates’s screams. “Get me out! Get me out of here!”

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Fonseca lifted her in his arms and ran to his car, parked behind a restaurant about a block away. Once there, a stranger helped lift Cates into the car while another stranger cleared a path through the terrified hordes and the emergency vehicles arriving at the scene.

Frantically driving the wrong way down Exeter and Beacon streets, Fonseca dodged police barricades and emergency workers as he sped the 2 miles to Massachusetts General Hospital, where nurses hurriedly moved Cates to the emergency room.

“I don’t know if I would have made it if I would have had to wait for the emergency workers,” Cates said in an interview Wednesday, her voice slightly broken as she battled tears. “He was an absolute hero.”

Two days after the Boston Marathon bombing that left three dead and more than 170 injured, shaken survivors continued to share tales of terror and panic. But as those stories emerge, so do others: of heroism.

As thousands fled the carnage, those near the blasts remember watching as dozens ran toward the chaos, looking to help however they could.

John Cowin, 65, of Leesburg, Fla., was waiting to see his daughter, a breast cancer survivor running in her third Boston Marathon, when the second blast struck directly across the street. Instinctively, he jumped over the divider meant to keep spectators off the street and dashed toward what seemed like a sea of maimed bodies. “It seems like there were more people hurt in the first bomb but that the extent of the injuries was more severe where we were,” said Cowin, an orthopedic surgeon. “It looked like a scene from Afghanistan.”

The first person he found was a father flailing in pain on the ground, his legs severed. Cowin said he tore off his belt, using it as a tourniquet as the man pleaded with him to check on his 3-year-old son, crying a few feet away.

Cowin picked up the terrified boy, who was bleeding but not seriously injured, and then flagged down a police officer who shepherded the child to safety. “We needed to get him out of there,” Cowin said. “We needed to keep him from seeing his father like that.”

Next, Cowin encountered two Boston University graduate students, one propped against a fence after being hit in the chest with shrapnel. Her friend lay unconscious a few feet away with a severe neck wound.

Cowin tended to the first, as paramedics began unsuccessful attempts to resuscitate her friend, later identified as Lingzi Lu. “I’ve been calling the consulate ever since,” Cowin said Wednesday. “If it will help them at all, I just want her family to know that she didn’t suffer.”

Even though he attended about half a dozen of the injured, Cowin rejects any characterization heralding him as a hero. Still, those hurt in the blasts insist it was volunteer first responders — in addition to hospital staffs — who saved lives.

“The police were doing the best they could, but it was other spectators who got to me first,” said Darrel Folkert, 42, of Redondo Beach, Calif., who suffered shrapnel injuries and burns to his legs as he waited to see his wife, running in her sixth marathon.

Folkert, who underwent surgery at Brigham and Women’s Hospital and is now back at home near Los Angeles, said spectators found him, carried him to safety, dressed his wounds, and helped him call his wife before handing him off to paramedics. “I can’t say enough how grateful I am for them,” Folkert said. “I was very fortunate.”

Still hospitalized in Boston, Cates said she has struggled to express her gratitude to the man she credits with saving her life. Fonseca, in turn, continues to monitor Cates’s medical progress, spending hours by her side in the hospital. Doctors saved Cates’s leg after a round of surgeries and have told her she will be able to walk again.

While relieved that she will recover, Cates and her boyfriend expressed a regret as they thought back to Monday’s madness. Fonseca recalled entering his girlfriend’s hospital room Tuesday night and finding her in tears. Was she in pain, or needing more medication, he wondered.

She shook her head no.

“I’m not crying for me,” he recalls her telling him softly. “I’m crying for everyone else who we weren’t able to help.”

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